The present invention relates to an electrostatic chuck used mainly in the semiconductor industry, and particularly to an electrostatic chuck which is thin, has small heat capacity and is excellent in the temperature rising/dropping property.
Semiconductors are very important products necessitated by various industries. Semiconductor chips are produced, for example, by first preparing a silicon wafer by slicing silicon single crystal at a predetermined thickness and then forming a plurality of integrated circuits and the like on the silicon wafer.
In the production process of semiconductor chips as described above, a semiconductor wafer such as a silicon wafer and the like is set on a device which allows various types of processing of the semiconductor wafer, and subjected to various types of processing including etching, CVD and the like, whereby integrated circuits, elements and the like are formed thereon.
When a semiconductor wafer is subjected to such processing, the semiconductor wafer must be firmly fixed to the device. For this reason, an electrostatic chuck inside of which electrostatic electrodes for attracting and firmly holding a semiconductor wafer are provided is generally employed.
As materials for constituting an electrostatic chuck, oxide ceramics such as alumina or nitride ceramics are used. In the case of an electrostatic chuck using ceramics as described above, electrostatic electrodes are formed on a ceramic substrate and a thin dielectric film is formed on each electrostatic electrode, so that the semiconductor wafer is adsorbed to the ceramic substrate by Coulomb force through the dielectric film.
In case that the hot CVD and the like is performed, as the semiconductor wafer needs to be heated, the electrostatic chuck is generally provided with a means for heating the ceramic substrate, such as a resistance heating element and the like.
In the electrostatic chuck using ceramics as described above, as Young""s modulus (strength) thereof is relatively large even at a high temperature, the thickness of the ceramic substrate can be made relatively thin and thus the weight of the electrostatic chuck can be characteristically reduced.
However, in recent years, as the size of semiconductor wafer becomes larger and the area of a ceramic substrate inevitably increases, the heat capacity of electrostatic chuck is getting higher. As a result, the temperature of a ceramic substrate is less likely to promptly follow the change in the voltage or current amount and the rate of temperature rising/dropping is slowed, whereby there arose a problem that the productivity of semiconductor wafers and the like is deteriorated.
Further, when a ceramic substrate of a relatively large size whose diameter exceeds 300 mm is used in order to adapt to a semiconductor wafer of 12 inches, the temperature tends to drop exceedingly at the periphery of the ceramic substrate, whereby there arose a problem that the temperature distribution on the heating face of the ceramic substrate is not even.
The present invention has been contrived in order to solve the above-mentioned problems. That is, one object of the present invention is to provide an electrostatic chuck which allows sufficiently rapid temperature rising/dropping thereof, in case that the diameter of a ceramic substrate exceeds 190 mm, or especially even in case that the diameter of the ceramic substrate is quite large, exceeding 300 mm.
As a result of the assiduous study for achieving the above-mentioned object, the inventors of the present invention have discovered that the temperature rising/dropping properties of a ceramic substrate can be prevented from deteriorating by reducing the thickness of the ceramic substrate to 20 mm or less and also reducing the heat capacity of the ceramic substrate. The present invention has been completed on the basis of this discovery.
That is, in a first aspect of the present invention, an electrostatic chuck comprises: a ceramic substrate equipped with a temperature controlling means; an electrostatic electrode formed on the ceramic substrate; and a ceramic dielectric film provided on the above-mentioned electrostatic electrode, wherein: the above-mentioned ceramic substrate has a diameter exceeding 190 mm and a thickness of 20 mm or less; and the above-mentioned ceramic dielectric film contains oxygen in an amount of 0.1 to 20 weight %.
According to the electrostatic chuck of the first aspect of the present invention, by reducing the thickness of the ceramic substrate to 20 mm or less, the temperature dropping at the peripheral portion of the ceramic substrate can be made as small as possible and the heat capacity thereof can be made small, even in case that the ceramic substrate has a relatively large size and the diameter thereof exceeds 190 mm. As a result, an electrostatic chuck which allows rapid temperature rising/dropping thereof can be realized.
When a ceramic substrate has a relatively large diameter, the ceramic substrate tends to deflect due to its own weight and thus a clearance is likely to be generated between the semiconductor wafer and the ceramic substrate, whereby heating of the semiconductor wafer evenly becomes difficult to be performed. Also, the thinner the substrate is, the more the substrate deflects.
However, in the above-mentioned ceramic dielectric film, as the dielectric film contains oxygen in an amount of 0.1 to 20 weight %, rigidity of the dielectric film is Improved so that the magnitude of flexure can be reduced.
In the electrostatic chuck of the first aspect of the present invention, it is preferable to use a resistance heating element as the above-mentioned temperature controlling means, because a resistance heating element can be formed in the electrostatic chuck relatively easily by: coating a conductor containing paste to a green sheet or a sintered body and subjecting the resultant to heating and firing; or embedding a metal wire in a formed body and subjecting the resultant to firing.
In a second aspect of the present invention, an electrostatic chuck comprises: a ceramic substrate equipped with a temperature controlling means; an electrostatic electrode formed on the ceramic substrate; and a ceramic dielectric film provided on the above-mentioned electrostatic electrode, wherein the above-mentioned ceramic substrate has a diameter exceeding 300 mm and a thickness of 20 mm or less.
In a case of a large type ceramic substrate whose diameter exceeds 300 mm, the area of the side face of the periphery thereof is relatively large and heat is easily lost there by being brought into contact with air. As a result, the temperature drop at the periphery of the ceramic substrate is large.
However, in the electrostatic chuck of the second aspect of the present invention, the thickness of the substrate is adjusted to 20 mm or less so that the contact area where the side face of the substrate is brought into contact with air decreases and heat is less likely to be released there and hence the temperature dropping at the peripheral portion can be made small. Also, the thickness of the substrate is adjusted to 20 mm or less so that the heat capacity thereof is made small. Thus, an electrostatic chuck which makes rapid temperature rising/dropping thereof possible is realized.
In the electrostatic chuck of the second aspect of the present invention, the above-mentioned ceramic dielectric film preferably contains oxygen in an amount of 0.1 to 20 weight %.
In case that the diameter of a ceramic substrate exceeds 300 mm, when the thickness of the substrate is made 20 mm or less, the ceramic substrate tends to deflect due to its own weight and thus a clearance is likely to be generated between the semiconductor wafer and the ceramic substrate, whereby even heating of the semiconductor wafer may become difficult to be performed and/or the chucking force may undesirably disperse. However, by setting the content of oxygen in the ceramic dielectric film in a range of 0.1 to 20 weight %, rigidity of the substrate is improved and thus the magnitude of flexure can be reduced.
Further, in the electrostatic chuck of the second aspect of the present invention, it is preferable to use a resistance heating element as the above-mentioned temperature controlling means, because a resistance heating element can be formed in the electrostatic chuck relatively easily by: coating a conductor containing paste to a green sheet or a sintered body and subjecting the resultant to heating and firing; or embedding a metal wire in a formed body and subjecting the resultant to firing.
Yet further, in the electrostatic chuck of the second aspect of the present invention, the thickness of the above-mentioned ceramic dielectric film is preferably in a range of 50 to 5000 xcexcm. When the thickness of the ceramic dielectric film is within in the above-mentioned range, the magnitude of flexure of the ceramic substrate can be reduced.
Incidentally, the publication of JP Kokai Hei 4-304942 discloses an electrostatic chuck which comprises a ceramic substrate whose thickness is 10 mm and diameter is 150 mm. However, in the case of this reference, the problem which the present invention tries to solve does not occur at all because the diameter of the substrate is quite small.
Also, the publication of JP Kokai Hei 7-86379 discloses an electrostatic chuck which includes a ceramic substrate whose thickness is 5 mm and diameter is 210 mm. However, in the case of this reference, the ceramic substrate thereof does not have sufficient rigidity because the content of yttria in the substrate is 2 weight % and this is small. As a result, the chucking force disperses in the electrostatic chuck.
Further, the publication of JP Kokai Hei 10-72260 discloses a ceramic substrate whose diameter is 200 mm and thickness is 12 mm. However, this reference makes no description of the oxygen content of the ceramic substrate.
In short, the above-mentioned references of the prior art are all related to a substrate whose diameter is smaller than 300 mm and irrelevant to the problem of temperature dropping at the periphery of the substrate.